Electromechanical vibrator



June l, 1943. r. A. READ 2,320,837

I ELECTROMECHANICAL VIBRATOR Filed July 24, 1941 WITNESSES: lNVENTORThomas f7. /Peaaf i Wa l ATTORNE Patented June 1, 1943 ELECTROMECHANICALVIBRATOR Thomas A. Read, Scarsdale, N. Y., assignor to WestinghouseElectric & Manufacturing Company, East Pittsburgh, Pa., a corporation ofPennsylvania Application July 24, 1941, serial No. 403,889

(Cl. 1v1-327) v9 Claims.

My invention relates to electro-mechanical vibrators and, in particular,relates to vibrators of this type which are adapted for determining thefrequency of alternating current in electrical circuits. Arrangements inwhich a crystal oi quartz or other material is embodied in the circuitof grid-controlled electron tubes and determines the frequency of radiocurrents flowing therethrough are well known, and my invention isapplicable, among other things, as a substiture for such quartzvibrators.

One object of my invention is to produce an electro-mechanical orpiezo-electric vibrator which shall have a relatively low and nearlyconstant impedance over a predetermined band of frequencies and whichshall have a much higher impedance outside said band of frequencies.'I'hls result is obtained by virtue of the rapid increase of thedecrement of the piezoelectric vibrator as the current flowing to itincreases.

Another object of my invention is to provide a method of tuning anelectric circuit so that a resonance curve is attained which risesabruptly at the lower limiting frequency, maintains a nearly? constantlevel until the vicinity of the higher frequency limit is reached andthen drops abruptly.

Still another object of my invention is to provide a coupling circuitfor superheterodyne and other radio apparatus in which the transmissionis much more nearly constant over 'the desired band of used frequencies,and which has a sharper drop-off at its limiting frequencies thanv dosimple circuits of the prior art.

Another object of my invention is to provide a band-pass iilter having aresonance curve much more nearly approaching the form of a rectanglethan do the resonance curves of present-day band-pass filters ofcorrespondingly simple construction.

The foregoing and other objects of my invention will become evident uponreading the following speciiication, taken in connection with thedrawing, in which:

Figure 1 illustrates the form of a typical resonance curve showing thevariation of electrical response with frequency of a present-daysuperheterodyne response with frequency of a presentday superheterodyneradio receiver;

Fig. 2` illustrates the form of resonance curve which would be ideal inthe operation of such a receiver;

F13. 3 is a view, partly in elevation and partly in section, of apiezo-electric vibrator in accordance with my invention;

Fig. 4 is an elevational view of a modified form of piezo-electricvibrator embodying my invention, and

5 is a schematic diagram of the coupling in one stage of an electrontube amplifier, said coupling embodying my invention.

It is Well known that for many purposes, particularly in the radio art,it is desired to obtain electrical circuits which will pass all currentsquite readily where they lie within a certain band, or range, offrequencies; but' which will transmit very little current when energizedby currents of frequency lying outside this band. So-called band-passiilters are an illustration of the type of circuit desired, and theseare too Well known in the radio art to require description here, Oneparticular field oi use of such circuits is in superheterodyne radiobroadcast receivers, inasmuch as the necessity for producing musicembodying a wide variety of pitches makes it necessary to transmit notonly the radio carrier wave, but a band of frequencies differingtherefrom by the frequency of the highest-pitch sound in the music beingreproduced.

In designing such electrical circuits, it is customary to plot curves ofthe type shown in Fig. l in which frequency of the electric circuit isabscissa and the amplitude of the transmitted current is plotted as theordinate; and circuits embodying capacitors shunted by pure inductances,or piezo-electric quartz crystalsvshunted by inductances, are found togive response curves of the general type of Fig. 1. It will be notedthat While such curves roughly delimit a band of frequencies throughoutwhich energy isl freely transmitted, the amplitude of the transmissionis by no means independent of the frequency throughout this band. Theideal form of resonance curve would be thatshown in Fig. 2 in which thetransmission is substantially zero below the lower marginal frequencyand also above the higher marginal frequency, and is substantiallyconstant between said marginal frequencies. In short, the ideal responsecurve is substantially rectangular in form.

I have discovered that by making a composite piezo-electric oscillator,or electro-mechanical vibrator, in which a portion cut from a singlecrystal of zinc is cemented or otherwise connected mechanically to aquartz lcrystal in the manner Cinnamon article describes the method ofproducing a single zinc lcrystal with a basal plane in any desireddirection. In accordance with my invention, I cut from such a singlezinc crystal a cylinder having its longitudinal axis at 45 degrees tothebasal plane. While the relationship of the vbasal plane just-mentionedis not absolutely required for proper operation f my compositeelement, Ihave found it preferable for many cases to employ this relationship. Ithen cut 'rom a piece of quartz a cylinder which may be of the samedimensions as the zinc piece just described, the electric axis of thequartz crystal being preferably perpendicular to the longitudinal axisof the quartz cylinder. I then cement one end of the zinc cylinder toone end of the quartz cylinder by some suitable agent, such, forexample, as De Khotinski cement which is well known in glass-blowingart. Electrodes, to which the electrical connections are made are thenaffixed to the faces of the quartz crystal which are perpendicular tothe electric axis. These electrodes are formed of metal, such, forexample, as silver, by electro-deposition or by the chemical methodsused in manufacturing mirrors, such methods being too well known torequire description here.

The composite element just described is then connected` into an electriccircuit, such, for example, as that illustrated in Fig. 5, or in any ofthe circuits which are now `Well known in the electrical art foremploying quartz piezo-electric crystals.

The arrangement shown in Fig. 3 I have found to be preferable where theaxis of the zinc cylinder is greater in length than its diameter, thecrystal axes having the directions indicated in this iigure. For certainfrequencies, it is more desirable that the axial length of the quartzcrystal shall be smaller than its diameter. In such cases, of which Fig.4 is illustrative, I make the Y-Y axis of the quartz perpendicular tothe axis of the cylinder, the electrical X-X axis of thequartz beingpreferably coincident with the latter. I then cut out from a single zinccrystal a cylinder preferably of the same dimensions as the quartz andhaving its basal plane at 45 degrees to its shortest dimension. I attachthe zinc and the quartz crystal to each other and provide them withconducting terminal-faces in the same way as has 4been described inconnection with Fig. 3.

In both Fig. 3 and Fig. 4, the cross-sections of the cylinder may besquare or, alternatively, may be circular or of other geometrical shape,so long as a cylindrical form is retained.

Fig. 5 illustrates an electrical circuit forming one stage of couplingof a radio amplifier. An input circuit supplies alternating currentthrough the primary winding of an input transformer, the

secondary winding, of which is shunted by a pair of capacitors C1 andC2, the mid-pointer which is preferably grounded. One terminal of thesecondary winding is connected through a capacitor C; to the primarywinding P of a second transformer. The other terminal of the secondarywinding is connected to one terminal plate of a composite crystal Z,such as I have described in connection with Fig. 3, the \other terminalplate being connected to the lead connecting capacitor C3 to the primarywinding P. 'I'he other terminal of the primary winding P is preferablygrounded. The secondary winding S which cooperates with the primarywinding P isshunted by a capacitor C4 and has one .terminal grounded.The other terminal is connected to the control grid of an ampliiler tubeA which feeds power in conventional ways to any desired output circuit.

To illustrate my invention more fully, I will state that the capacitorsC1 and C2 each may be approximately micro-microfarads. The capacitor C3may be approximately 10 to 100 micromicrofarads, its value being such asto balance the capacity between the electrodes in the vibrator Z. Thecapacitor C4 and the secondary winding S are tuned substantially to thefrequency mid- -way between the operative limits of the response curveof the composite crystal.

Referring to Fig. 3, the zinc member and the l quartz member may each bea cylinder approximately one-half an inch long and one-quarter inchsquare. Such a composite member would have a passing-band extending fromapproximately 200,000 cycles to 202,000 cycles per second. Referring toFig. 4, the quartz plate and the zinc plate may each be approximatelygth of an inch thick and one inch square. 4

While I have described my invention as embodying a quartz crystal inconjunction with the zinc member, it will be recognized by those skilledin the artthat other well known piezo-electric materials may besubstituted for the quartz when conditions make such other material moredesirable. It will also be recognized that while I have described theuse of a member cut from a single crystal of zinc, it may be desirableto substitute portions of single crystals or other forms made up ofother metals.` It will also be recognized by o those skilled in the artthat while I have described my electro-mechanical vibrator in connectionwith radio circuits, it is of application wherever electro-mechanicalvibrators or piezoelectric devices having response-curves approximatingthe rectangle in form are desired.

I claim as my invention:

l. In combination with an electric circuit, an electro-mechanicalvibrator comprising a piezoelectric crystal mechanically linked to asingle crystal of zinc. A

2. In combination with an electric circuit, an electro-mechanicalvibrator comprising a piezoelectric crystal mechanically linked to asingle crystal of zinc, the basal plane of the zinc crystal beingapproximately forty-five degrees to the electrical axis of thepiezo-electric crystal.

3. In combination with an electric circuit, an electro-mechanicalvibrator comprising a quartz crystal mechanically linked to a singlecrystal of zinc.

4. In combination with an electric circuit, an electro-mechanicalvibrator comprising a quartz crystal mechanically linked to a singlecrystal of zinc, the basal plane of the zinc crystal being approximatelyforty-five degrees to the electrical axis of the quartz crystal.

5. A mechanical structure comprising a single zinc crystal mechanicallylinked to a piezo-electric crystal.

6. A mechanical structure comprising a single connected at one end to asubstantially similar cylinder cut from a piezo-electric crystal.

9. A mechanical structure comprising a cylinder cut from a singlecrystal of zinc mechanically connected at one end to a substantiallysimilar cylinder cut from a piezo-electric crystal, the basal plane ofthe zinc being at forty-five degrees l to the cylindrical axis.

der cut from a single crystal of zinc mechanically l0 THOMAS A. READ.

